(TiVZrNb)83Cr17 high-entropy alloy as catalyst for hydrogen storage in MgH2

Abstract

High-entropy alloys (HEAs) hold the promise as excellent catalysts to improve the hydrogen storage properties of MgH2 due to their distinctive compositional and structural characteristics and superior room-temperature hydrogen storage performance. In this work, the (TiVZrNb)83Cr17 HEA was successfully designed and synthesized. Moreover, different amounts of the (TiVZrNb)83Cr17 HEA were introduced into MgH2 as catalysts by ball milling to prepare MgH2-x wt% (TiVZrNb)83Cr17 (x = 3, 6, 10) composites. MgH2-6 wt% (TiVZrNb)83Cr17 composite showed excellent hydrogen absorption and desorption properties. At 573 K, the composite can rapidly absorb 5.3 wt% H2 within 5 min, and even at 523 K, it can still absorb 4.0 wt% H2 within 60 min. Also, it can rapidly desorb 6.0 wt% and 4.1 wt% H2 within 60 min at 623 K and 573 K, respectively. In addition, the MgH2-6 wt% (TiVZrNb)83Cr17 composite possessed relatively low activation energy for hydrogen absorption (70.6 kJ/mol H2) and desorption (90.5 kJ/mol H2). Moreover, the capacity retention was as high as 98.5 % after 10 hydrogen de/absorption cycles at 573 K. Interestingly, (TiVZrNb)83Cr17 HEA transformed from the as-prepared biphasic structure (FCC + BCC) to the hydrogenated single-phase structure (FCC) in the hydrogenation process and returned to the initially biphasic structure (FCC + BCC) in the desorption process, which provided more diffusion pathways for H and more nucleation sites for Mg/MgH2. The multi-element (TiVZrNb)83Cr17 HEA catalyst realized the synergistic catalysis of the hydrogen ab/de-sorption of Mg/MgH2. Our findings provide useful insights into the design and development of HEAs catalysts for improving the hydrogen storage properties of MgH2.